1. Field of the Invention
The present invention relates to a substrate inspection device and a substrate inspecting method for inspecting discontinue or open-circuit state and a short-circuit state of wirings formed on a substrate by selecting a wiring one by one from the plural wirings formed on the substrate subject to inspection, and by detecting a value of a current flowing through the selected wiring or a wiring adjacent to the selected wiring. The invention is applicable to an inspection of electrical wirings on various substrates, including a printed circuit board, a flexible circuit film, a multi-layer wiring board, an electrode plate used in a liquid crystal display or a plasma display device, and a packaging substrate or a film carrier used in a semiconductor package. Hereinafter, these various wiring boards are collectively referred to as the substrates.
2. Related Art
Many types of substrate inspection devices have been provided to examine whether wirings or wirings on a substrate are formed exactly as designed. In particular, as electric and electronic devices are made smaller in size in recent years, the wirings on a substrate used in such a device is required to be fine and to be arranged at high density, and lands of the wirings used as inspection points are increasing in number while decreasing in width. This makes it difficult to conduct an inspection of wirings for a open or a short-circuit by bringing probes of the inspection device into direct contact with all the inspection points on the lands or wirings. To solve this problem, there is proposed a substrate inspection device that inspects wirings for a open or a short-circuit without contact of probes with the lands or wirings.
For example, a substrate inspection device that uses electrons generated by irradiating laser beams onto the lands has been proposed in U.S. Pat. No. 6,777,949 of which disclosure is incorporated herein by reference. The patent discloses an embodiment that inspects the substrate using a current produced by irradiating a laser beam in the UV range to one end of a wiring subject to inspection, and by trapping by a plus electrode electrons released from the irradiated one end of the wiring due to the photo-electric effect.
The device described in the patent enables the inspection of wirings for a open or a short-circuit without contact of the probe to the lands on one side of the substrate. However, because this device makes use of the photo-electric effect, the wavelength of a laser beam to be irradiated is limited up to a specific value (referred to as the threshold wavelength), which may possibly increase the manufacturing costs of the substrate inspection device. In addition, because the threshold wavelength varies with materials (gold copper, etc.) forming the wirings (lands), the wavelength of a laser beam to be irradiated needs to cover the materials forming the lands or wirings, resulting in limitation of the laser beam to be used.